Array geometry, size and spacing effects on field emission characteristics of aligned carbon nanotubes

摘要

Microwave plasma-enhanced chemical vapor deposition (MPECVD) has been shown capable of producing vertically aligned mutli-walled CNTs as a result of self-bias of the microwave plasma. These CNTs are relevant to field emission applications. However, it is also known that closely packed or mat-like CNTs are not effective field emitters due to field screening effects among neighboring tubes. In this study, an approach whereby "micro-" patterning of CNT arrays, adjusting their geometry, size and array spacing by conventional photo lithography, rather than "nano-" patterning a single CNT by electron-beam lithography, is employed to fabricate efficient emitters with enhanced field emission characteristics. MPECVD with catalysts are used on Si substrate to fabricate micropattemed vertically aligned CNT arrays with various geometries, sizes and spacing. The field emission results show that a circular array with 20 mu m spacing has the lowest tum-on field of approx 2 V/mu m at 1 mu A/cm~2 and achieves the highest current density of 100 uA/cm~2 at approx 3 V/mu m. Investigation on the array spacing effect shows that 10X10 mu m CNT square array with an array spacing of 20 mu m displays the lowest tum-on field of ~9 V/mu m and achieved a very high current density of approx 100 mA/cm~2 at approx 20 VI mu m. Furthermore, the results suggest that the array spacing of the 10 X 10 mu m CNT square array can be reduced to at least 20 mu m without affecting the field enhancement factor of the emitter. The results clearly indicate further optimization of spacing in the arrays of CNT emitters could result in lower tum-on field and higher current density.